The present invention relates to a quantum well device and a method of forming the same, and more particularly, to a quantum well device with electro-static discharge (ESD) endurance and a method of forming the same.
For recent years, a multiple quantum well structure has been extensively applied in the light emitting semiconductor structure. Various improved multiple quantum well structures have been also researched and developed. A modern multiple quantum well structure is frequently applied to a light emitting diode or a laser diode.
FIG. 1 is a schematic diagram of a conventional quantum well device 10. The conventional quantum well device 10 includes a GaAs substrate 12 of a first conductivity type and a GaAs buffer layer 14 on the GaAs substrate 12. An AlGaInP cladding layer 16 of the first conductivity type is formed on the GaAs buffer layer 14. A lower confining layer 18 is formed on the AlGaInP cladding layer 16. An active layer 20 is formed on the lower confining layer 18. An upper confining layer 22 is formed on the active layer 20. An AlGaInP cladding layer 24 of a second conductivity type is formed on the upper confining layer 22. Finally, a cover layer 26 of the second conductivity type is formed on the AlGaInP cladding layer 24, wherein the cover layer 26 is a window layer or an ohmic contact layer.
FIG. 2 is a schematic diagram of the active layer 20 shown in FIG. 1. The active layer 20 of the conventional quantum well device 10 adopts a multiple quantum layers structure which is formed by alternately stacking a plurality of barrier layers 19 and a plurality of quantum well layers 21. Each barrier layer 19 and each quantum well layer 21 are made of undoped AlGaInP.
FIG. 3 is an ESD performance test diagram of the quantum well device 10 shown in FIG. 1. For a long time, ESD problems coming from human-body mode or machine mode have existed in the quantum well device 10. Particularly for the quantum well device 10 having an emitting light wavelength between 570 nm and 650 nm, the accumulated failure percentage of the quantum well device 10 nears almost 100% if a failure voltage resulting from ESD is raised from 0V to 3 kV according to the ESD performance test results. Therefore, U.S. Pat. No. 5,116,767 discloses a laser diode having a passivation layer to improve the electric stress induced by artificial or mechanical ESD. However, the passivation layer places burden over the technology of epitaxy process and increases cost. Therefore it is not widely applied.
To overcome the above problems, the present invention discloses a quantum well device and a method of forming the same. The quantum well device includes alternately stacked n layers of quantum well layers and n layers of barrier layers, wherein the quantum well layers and barrier layers are alternatively doped with dopant, and n is a positive integer. The quantum well device of the above structure is usually referred to as an active layer in a light emitting device.
The method of forming a quantum well device includes the steps of alternately stacking n layers of quantum well layers and n layers of barrier layers, and during the stacking step, alternatively doping the quantum well layers and barrier layers with dopant, wherein n is a positive integer.
In other embodiments, the quantum well device further includes a substrate, a buffer layer, a lower cladding layer, a lower confining layer, an upper confining layer, an upper cladding layer, and a cover layer.
The dopant of the quantum well device controls the breakdown voltage and output intensity of the quantum well device and consequently avoids artificial and mechanical ESD failure. In embodiments, the dopant is n-type dopant including Te, Se or Si. In another embodiments, the dopant is p-type dopant including Mg, C or Zn. A concentration of the dopant is preferably between 5xc3x97106/c.c and 3xc3x971018/c.c.